Fluorocarbon based fluids have found widespread use in many commercial and industrial applications, including as the working fluid in systems such as air conditioning, heat pump and refrigeration systems, among other uses such as aerosol propellants, as blowing agents, and as gaseous dielectrics.
Heat transfer fluids, to be commercially viable, must satisfy certain very specific and in certain cases very stringent combinations of physical, chemical and economic properties. Moreover, there are many different types of heat transfer systems and heat transfer equipment, and in many cases it is important that the heat transfer fluid used in such systems possess a particular combination of properties that match the needs of the individual system. For example, systems based on the vapor compression cycle usually involve the phase change of the refrigerant from the liquid to the vapor phase through heat absorption at a relatively low pressure and compressing the vapor to a relatively elevated pressure, condensing the vapor to the liquid phase through heat removal at this relatively elevated pressure and temperature, and then reducing the pressure to start the cycle over again.
Certain fluorocarbons, for example, have been a preferred component in many heat exchange fluids, such as refrigerants, for many years in many applications. Fluoroalkanes, such as chlorofluoromethanes and chlorofluoroethanes, have gained widespread use as refrigerants in applications including air conditioning and heat pump applications owing to their unique combination of chemical and physical properties, such as heat capacity, flammability, stability under the conditions of operation, and miscibility with the lubricant (if any) used in the system. Moreover, many of the refrigerants commonly utilized in vapor compression systems are either single components fluids, or zeotropic, azeotropic mixtures.
Concern has increased in recent years about potential damage to the earth's atmosphere and climate, and certain chlorine-based compounds have been identified as particularly problematic in this regard. The use of chlorine-containing compositions (such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and the like) as refrigerants in air-conditioning and refrigeration systems has become disfavored because of the ozone-depleting properties associated with many of such compounds. There has thus been an increasing need for new fluorocarbon and hydrofluorocarbon compounds that offer alternatives for refrigeration and heat pump applications. By way of example, in certain aspects, it has become desirable to retrofit chlorine-containing refrigeration systems by replacing chlorine-containing refrigerants with non-chlorine-containing refrigerant compounds that will not deplete the ozone layer, such as hydrofluorocarbons (HFCs).
Another concern surrounding many existing refrigerants is the tendency of many such products to cause global warming. This characteristic is commonly measured as global warming potential (GWP). The GWP of a compound is a measure of the potential contribution to the green house effect of the chemical against a known reference molecule, namely, CO2 which has a GWP=1. For example, the following known refrigerants possess the following Global Warming Potentials:
REFRIGERANTGWP (IPCC AR5)R410A2088R-5073985R404A3943R407C1774
While each of the above-noted refrigerants has proven effective in many respects, these materials are become increasingly less preferred since it is frequently undesirable to use materials having relatively high GWP. A need exists, therefore, for substitutes for these and other existing refrigerants having undesirable GWPs.
There has thus been an increasing need for new fluorocarbon and hydrofluorocarbon compounds and compositions that are attractive alternatives to the compositions heretofore used in these and other applications. For example, it has become desirable to retrofit certain systems, including chlorine-containing and certain HFC-containing refrigeration systems by replacing the existing refrigerants with refrigerant compositions that will not deplete the ozone layer, will not cause unwanted levels of global warming, and at the same time will satisfy all of the other stringent requirements of such systems for the materials used as the heat transfer material.
With respect to performance properties, the present applicants have come to appreciate that that any potential substitute refrigerant must also possess those properties present in many of the most widely used fluids, such as excellent heat transfer properties, chemical stability, low- or no-toxicity, low or non-flammability and lubricant compatibility, among others.
With regard to efficiency in use, it is important to note that a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy.
Furthermore, it is generally considered desirable for refrigerant substitutes to be effective without major engineering changes to conventional vapor compression technology currently used with existing refrigerants, such as CFC-containing refrigerants.
Flammability is another important property for many applications. That is, it is considered either important or essential in many applications, including particularly in heat transfer applications, to use compositions which are non-flammable or of relatively low flammability. As used herein, the term “nonflammable” refers to compounds or compositions which are determined to be nonflammable as determined in accordance with ASTM standard E-681, dated 2002, which is incorporated herein by reference. Unfortunately, many HFC's which might otherwise be desirable for used in refrigerant compositions are highly flammable. For example, the fluoroalkane difluoroethane (HFC-152a) is flammable and therefore not viable for use alone in many applications.
Applicants have thus come to appreciate a need for compositions, and particularly heat transfer compositions, that are potentially useful in numerous applications, including vapor compression heating and cooling systems and methods, while avoiding one or more of the disadvantages noted above.